A device having a high speed and broad dynamic range has been required in communications using POF (plastic optical fiber).
A photodetection used in such an application has been required.
Conventionally, it has been hitherto widely known that a feedback circuit is used for a current-voltage converting amplifier for converting a current output of a photodetecting element to a voltage to broaden the dynamic range (see Patent Document 1).
Furthermore, there is also known a receiving circuit of an optical coupling device in which a dummy photodiode is provided to shape the waveform, thereby enhancing a common mode noise rejection ratio. Specifically, it is known that the outputs of the photodiode for photodetecting and the light-shielded photodiode are subjected to gain adjustment, and then the difference therebetween is taken to carry out photodetection (see Patent Document 2).
There is also known a circuit having control means for varying the output of a second photodetecting element to incident light corresponding to the output from a first photodetecting element (see Patent Document 3).
There is known a device in which a light input is branched to two output parts, one output part is delayed and then applied to a photodetecting element while the other output part is applied to another photodetecting element, and when the output voltage thereof or the output voltage of a photodetecting element contained in an optical amplifier exceeds a reference value, the bias voltage of the photodetecting element is lowered, an attenuator is controlled to lower the input light to the photodetecting element, or the output light of the optical amplifier is attenuated and applied to APD as the photodetecting element concerned (see Patent Document 4).
Furthermore, there is also known a construction that in order to enlarge the dynamic range and save the power consumption, a current output from a photodetecting element is monitored by a monitor circuit, the monitored value is compared with a predetermined reference value to judge whether the photodetection level is larger or smaller than an appropriate value, and any one of a through circuit constituting a multi-stage amplifier connected to the photodetecting element or a gain adjusting amplifying circuit on the basis of the above judgment result. Furthermore, there is provided a construction in which the output of a monitor circuit is applied to a variable gain type initial stage amplifying circuit to enable the gain control corresponding to the photodetection level (see Patent Document 5).
Patent Document 1: Japanese Published Unexamined Patent Application No. 2-143731
Patent Document 2: Japanese Published Unexamined Patent Application No. 2002353495
Patent Document 3: Japanese Published Unexamined Patent Application No. 2000-200922
Patent Document 4: Japanese Published Unexamined Patent Application No. 11-41180
Patent Document 5: Japanese Published Unexamined Patent Application No. 10-107738